In motor vehicles, it is a general goal to reduce the effects of a collision on the occupants of the vehicle as much as possible. In today's cars, three-point seatbelts are therefore normally employed to restrain the occupants of the vehicle. In a known manner, the seatbelts offer good protection and increased safety for the occupants should a collision take place.
Nowadays, there is also a desire to provide steering systems in vehicles which are energy-absorbing. The reason for this desire, which is dictated by legislation in certain countries, is that there is a need to offer some degree of protection to a driver who is not wearing a seatbelt when he is thrown towards the steering wheel in a collision.
It is previously known to design the steering system of the vehicle so that it absorbs energy when the driver of the car is thrown forwards and impacts the steering wheel during a collision. This can be achieved, for example, by designing the steering wheel with deformable and flexible spokes. This can also be achieved by arranging the steering shaft of the vehicle in a particularly designed energy absorbing steering column which is attached to the stress-bearing structure of the vehicle. In the event of a collision, when the steering wheel, and thus also the steering column, are influenced by a very large force as a result of the occupant being thrown forwards, this force will be transmitted from the steering wheel to the steering column. In this manner, the steering column will be displaced a certain distance relative to the vehicle structure. During this displacement, energy will be absorbed which, as a consequence, reduces the effects on the driver during the collision sequence.
Apparatus is disclosed in U.S. Pat. No. 4,978,138 for energy absorption in a steering system for vehicles. This apparatus is based on the principle that if the driver is not wearing his seatbelt, the steering system will absorb energy when the driver is thrown against the steering wheel during a possible collision. To achieve this, the arrangement includes a particular deformable and energy-absorbing bracket which is connected to the steering column. In order to determine whether the driver is wearing his seatbelt, a sensor is arranged on the seatbelt lock. This known arrangement also includes means for protecting the driver's knees, which means is activated irrespective of whether the driver is wearing his seatbelt or not. If the driver is wearing his seatbelt, the force from the knees will be absorbed by the knee protector as the steering wheel is displaced, whereby it is possible to prevent the upper body and head of the driver from impacting the steering wheel. The arrangement according to this patent, however, suffers from the disadvantage that the circumstances in which the driver can in fact impact the steering wheel during a collision even if he is wearing his seatbelt are not taken into account. This can occur, for example, when the driver has his seat in a well forward position or when the seatbelt is unusually slack.